Showing papers by "Christian V. Stevens published in 2021"

Continuous Flow Synthesis of Metal–NHC Complexes**

Abstract: The use of weak bases and mild conditions is currently the most sustainable and attractive synthetic approach for the preparation of late-transition metal complexes, some of which are widely used in catalysis, medicinal chemistry and materials science. Herein, the use of cuprate, aurate or palladate species for a continuous flow preparation of CuI , AuI and PdII -NHC complexes is reported. All reactions examined proceed under extremely mild conditions and make use of technical grade acetone as solvent. The scalability of the process was exemplified in a multigram-scale synthesis of [Cu(IPr)Cl].

Overview of N-Rich Antennae Investigated in Lanthanide-Based Temperature Sensing.

Abstract: The market share of noncontact temperature sensors is expending due to fast technological and medical evolutions. In the wide variety of noncontact sensors, lanthanide‐based temperature sensors stand out. They benefit from high photostability, relatively long decay times and high quantum yields. To circumvent their low molar light absorption, the incorporation of a light‐harvesting antenna is required. This review provides an overview of the nitrogen‐rich antennae in lanthanide‐based temperature sensors, emitting in the visible light spectrum, and discuss their temperature sensor ability. The N‐rich ligands are incorporated in many different platforms. The investigation of different antennae is required to develop temperature sensors with diverse optical properties and to create a diverse offer for the multiple application fields. First the molecular probes, consisting of small molecules, are discussed. Furthermore, the thermometer properties of ratiometric temperature sensors, based on di‐ and polynuclear complexes, metal‐organic‐frameworks, periodic mesoporous organosilicas and porous organic polymers, are summarized. The antenna mainly determines the application potential of the ratiometric thermometer. It can be observed that molecular probes are operational in the broad physiological range, metal‐organic‐frameworks are generally very useful in the cryogenic region, periodic mesoporous organosilica show temperature dependency in the physiological range and porous organic polymers are operative in the cryogenic to medium temperature range.

Arabidopsis Hypocotyl Adventitious Root Formation Is Suppressed by ABA Signaling

Abstract: Roots are composed of different root types and, in the dicotyledonous Arabidopsis, typically consist of a primary root that branches into lateral roots. Adventitious roots emerge from non-root tissue and are formed upon wounding or other types of abiotic stress. Here, we investigated adventitious root (AR) formation in Arabidopsis hypocotyls under conditions of altered abscisic acid (ABA) signaling. Exogenously applied ABA suppressed AR formation at 0.25 µM or higher doses. AR formation was less sensitive to the synthetic ABA analog pyrabactin (PB). However, PB was a more potent inhibitor at concentrations above 1 µM, suggesting that it was more selective in triggering a root inhibition response. Analysis of a series of phosphonamide and phosphonate pyrabactin analogs suggested that adventitious root formation and lateral root branching are differentially regulated by ABA signaling. ABA biosynthesis and signaling mutants affirmed a general inhibitory role of ABA and point to PYL1 and PYL2 as candidate ABA receptors that regulate AR inhibition.

Learning Molecular Representations for Thermochemistry Prediction of Cyclic Hydrocarbons and Oxygenates.

Abstract: Accurate thermochemistry estimation of polycyclic molecules is crucial for kinetic modeling of chemical processes that use renewable and alternative feedstocks. In kinetic model generators, molecular properties are estimated rapidly with group additivity, but this method is known to have limitations for polycyclic structures. This issue has been resolved in our work by combining a geometry-based molecular representation with a deep neural network trained on ab initio data. Each molecule is transformed into a probabilistic vector from its interatomic distances, bond angles, and dihedral angles. The model is tested on a small experimental dataset (200 molecules) from the literature, a new medium-sized set (4000 molecules) with both open-shell and closed-shell species, calculated at the CBS-QB3 level with empirical corrections, and a large G4MP2-level QM9-based dataset (40 000 molecules). Heat capacities between 298.15 and 2500 K are calculated in the medium set with an average deviation of about 1.5 J mol−1 K−1 and the standard entropy at 298.15 K is predicted with an average error below 4 J mol−1 K−1 . The standard enthalpy of formation at 298.15 K has an average out-of-sample error below 4 kJ mol−1 on a QM9 training set size of around 15 000 molecules. By fitting NASA polynomials, the enthalpy of formation at higher temperatures can be calculated with the same accuracy as the standard enthalpy of formation. Uncertainty quantification by means of the ensemble standard deviation is included to indicate when molecules that are on the edge or outside of the application range of the model are evaluated

Continuous Flow Synthesis of [Au(NHC)(Aryl)] (NHC=N-Heterocyclic Carbene) Complexes

Abstract: The use of weak and inexpensive bases has recently opened promising perspectives towards the simpler and more sustainable synthesis of Au(I)-aryl complexes with valuable applications in catalysis, medicinal chemistry, and materials science. In recent years, continuous manufacturing has shown to be a reliable partner in establishing sustainable and controlled process scalability. Herein, the first continuous flow synthesis of a range of Au(I)-aryl starting from widely available boronic acids and various [Au(NHC)Cl] (NHC=N-heterocyclic carbene) complexes in unprecedentedly short reaction times and high yields is reported. Successful synthesis of previously non- or poorly accessible complexes exposed fascinating reactivity patterns. Via a gram-scale synthesis, convenient process scalability of the developed protocol was showcased.

Quantifying the Likelihood of Structural Models through a Dynamically Enhanced Powder X‐Ray Diffraction Protocol

Abstract: Structurally characterizing new materials is tremendously challenging, especially when single crystal structures are hardly available which is often the case for covalent organic frameworks. Yet, knowledge of the atomic structure is key to establish structure-function relations and enable functional material design. Herein, a new protocol is proposed to unambiguously predict the structure of poorly crystalline materials through a likelihood ordering based on the X-ray diffraction (XRD) pattern. Key of the procedure is the broad set of structures generated from a limited number of building blocks and topologies, which is submitted to operando structural characterization. The dynamic averaging in the latter accounts for the operando conditions and inherent temporal character of experimental measurements, yielding unparalleled agreement with experimental powder XRD patterns. The proposed concept can hence unquestionably identify the structure of experimentally synthesized materials, a crucial step to design next generation functional materials.

Cytosolic delivery of gadolinium via photoporation enables improved in vivo magnetic resonance imaging of cancer cells.

Abstract: Longitudinal in vivo monitoring of transplanted cells is crucial to perform cancer research or to assess the treatment outcome of cell-based therapies. While several bio-imaging techniques can be used, magnetic resonance imaging (MRI) clearly stands out in terms of high spatial resolution and excellent soft-tissue contrast. However, MRI suffers from low sensitivity, requiring cells to be labeled with high concentrations of contrast agents. An interesting option is to label cells with clinically approved gadolinium chelates which generate a hyperintense MR signal. However, spontaneous uptake of the label via pinocytosis results in its endosomal sequestration, leading to quenching of the T1-weighted relaxation. To avoid this quenching effect, delivery of gadolinium chelates directly into the cytosol via electroporation or hypotonic cell swelling have been proposed. However, these methods are also accompanied by several drawbacks such as a high cytotoxicity, and changes in gene expression and phenotype. Here, we demonstrate that nanoparticle-sensitized laser induced photoporation forms an attractive alternative to efficiently deliver the contrast agent gadobutrol into the cytosol of both HeLa and SK-OV-3 IP1 cells. After intracellular delivery by photoporation the quenching effect is clearly avoided, leading to a strong increase in the hyperintense T1-weighted MR signal. Moreover, when compared to nucleofection as a state-of-the-art electroporation platform, photoporation has much less impact on cell viability, which is extremely important for reliable cell tracking studies. Additional experiments confirm that photoporation does not induce any change in the long-term viability or the migratory capacity of the cells. Finally, we show that gadolinium ‘labeled’ SK-OV-3 IP1 cells can be imaged in vivo by MRI with high soft-tissue contrast and spatial resolution, revealing indications of potential tumor invasion or angiogenesis.

Endocrine disrupting potency and toxicity of novel sophorolipid quaternary ammonium salts

Abstract: A new class of biosurfactants, namely quaternary ammonium sophorolipids (SQAS), suitable for pharmaceutical applications, was tested for the evaluation of their (anti)estrogenic and (anti)androgenic potency with the help of YES/YAS assays. Also their toxicity towards yeasts (Saccharomyces cerevisiae) and bacteria (Escherichia coli) was checked. The results achieved for SQAS, which can be regarded as potential micropollutants, were compared with those obtained for two well-known micropollutants diclofenac and 17α-ethinylestradiol subjected to the same testing procedures. This work demonstrated that acetylation of the hydroxyl group of the carbohydrate head of SQAS decreased the toxicity of this class of biosurfactants towards Saccharomyces cerevisiae. Furthermore, it contributed to the decrease of their endocrine disrupting potency. None of the SQAS studied showed clear agonist activity for female or male hormones. SQAS1 and SQAS2 revealed weak antiestrogenic and antiandrogenic potency. All of these properties were weaker, not only to the potency of the appropriate positive control in the antagonists bioassays, but also compared to the potency of other tested compounds, i.e. DCF and EE2. SQAS3 possessed most probably inhibitory activity towards male hormones. Moreover, cytotoxicity of two out of four studied SQAS at the highest concentrations towards the strains of Saccharomyces cerevisiae interfered with the endocrine disruption activity. It would be also worth studying it with the use of another endocrine activity test.

Enzymatic Degumming of Rice Bran Oil Using Different Commercial Phospholipases and Their Cocktails

Abstract: Rice bran oil is a highly nutritious vegetable oil, as it is rich in tocols and γ-oryzanol. Degumming is the first step in the vegetable oil refining process, and its main objective is the removal of phospholipids or gums. In the present study, enzymatic degumming trials were performed on crude rice bran oil using the phospholipases PLA1, Purifine® PLC, their mixture (PLA1/PLC), and a cocktail known as Purifine® 3G. Enzymatic degumming applying 50 mg/kg of PLA1 for 120 min resulted in a residual phosphorus content of 10.4 mg/kg and an absolute free fatty acid increase of 0.30%. Enzymatic degumming applying 300 mg/kg of Purifine® PLC for 120 min at 60 °C resulted in a residual phosphorus content of 67 mg/kg and an absolute diacylglycerol increase of 0.41%. The mixture of phospholipases and the cocktail presented approximately 5 mg/kg of residual phosphorus content after the reaction times. For all degumming processes, the preservation of minor components such as tocols and γ-oryzanol were observed. These results indicate that the use of enzyme mixtures or their cocktails to attain low phosphorus content and high diacylglycerol/free fatty acid conversion during enzymatic degumming is a viable alternative.

Heterogeneous Catalyzed Chemoselective Reductive Amination of Halogenated Aromatic Aldehydes

Abstract: The chemoselective conversion of a specific functional group in a multifunctional substrate is of great importance in the chemical industry to obtain cost efficient, sustainable and waste free processes. This work focuses on the chemoselective amination of halogenated aromatic aldehydes with dimethyl amine towards halogenated aromatic amines, a raw material used in the production of for example agrochemical active ingredients. It was found that by combining palladium, a metal known for dehalogenation reactions, and copper, known for its direct hydrogenation of aldehydes to alcohols, in one heterogeneous bimetallic catalyst, a synergistic effect is obtained. By depositing copper onto a palladium on carbon catalyst with a Cu/Pd ratio of at least 1 : 1, the yield could be increased from 66 % (Pd/C) to 98 % (PdCu/C). Moreover, this highly active and stable catalyst also showed suppressed dehalogenation side‐reactions in several other chemical conversions such as hydrogenation of nitro functional groups and hydrogenation of aldehydes.

Synthesis of nitrile-functionalized polydentate N-heterocycles as building blocks for covalent triazine frameworks

Abstract: Covalent triazine frameworks (CTFs) based on polydentate ligands are highly promising supports to anchor catalytic metal complexes. The modular nature of CTFs allows to tailor the composition, structure, and function to its specific application. Access to a broad range of chelating building blocks is therefore essential. In this respect, we extended the current available set of CTF building blocks with new nitrile-functionalized N-heterocyclic ligands. This paper presents the synthesis of the six ligands which vary in the extent of the aromatic system and the denticity. The new building blocks may help in a rational design of enhanced support materials in catalysis.

Effect of Newly Synthesized Salts and Three Common Micropollutants on the Biochemical Activity of Nitrifiers

Abstract: Often, different types of contaminants in wastewater are suspected of adversely affecting the treatment efficiency of a wastewater treatment plant (WWTP). Therefore, it is essential to study the effects of newly synthesized substances on the activity of activated sludge microorganisms. The aim of this study was to determine the effect of innovative biosurfactants, i.e., sophorolipids quaternary ammonium salts (SQAS), and three common micropollutants (MPs), i.e., diclofenac (DCP), 17α-ethynylestradiol (EE2), and 4-nonylenol (4-NP), on the biochemical activity of activated sludge microorganisms. The effect of all tested substances was more significant on nitrite-oxidizing bacteria (NOB) than on ammonia-oxidizing bacteria (AOB), and least on the respiratory activity of heterotrophic organisms (HET). SQAS inhibited nitrification even at the lowest concentration tested (5 mg L−1) and the inhibition degree was in the range of 37% to 78%; at the highest concentration of SQAS studied (160 mg L−1), it was about 45–96%. In most cases, the degree of inhibition increased when the SQAS concentration approached 80–160 mg L−1. MPs influenced the activity of nitrifiers to a lower extent than SQAS. The inhibition degree varied from 25% to 75%, depending on the micropollutant tested and its concentration.